[david-given]

I have a port of Alan Cox's Fuzix for the MSP430 where the entire bootable ROM image is 27kB.

(That's actually quite big for a tiny-computer OS, although it's the smallest Unix I know of.)

[DiabloD3]

For those who don't know who Alan Cox is, he was the Linux 2.2 branch maintainer, is still heavily involved in Linux, and also does lots of other neat shit.

[cbsmith]

I seem to recall the QNX kernel is pretty slim as well.

[pjc50]

I used to have a 1.44Mb floppy that booted QNX to a desktop environment. Of course, that's not so unusual historically: both Amiga and GEM had single-floppy desktop enviroments (or did the Amiga require two to get to Workbench?)

[david-given]

That's just the microkernel, though --- it didn't contain any functionality other than sending messages (and a few other things, microkernels very).

Fuzix' 27kB contains the scheduler, drivers, tty, file system and Posix subsystem!

[cbsmith]

Fuzix definitely was end to end. On the other hand, the QNX kernel is a more capable foundation to build on.